A method as described above is for example disclosed in United States Patent application number US 2002/0127824, by Shelton et. al., disclosing the removal of slag from semiconductor elements separated from a wafer using a laser dicing method. The document concentrates on the removal of slag from devices which are manufactured by separating them from a wafer, using a laser ablation scribing process for forming scribing lines followed by a step of breaking the wafer along these scribing lines. In particular, the slag is removed from the wafer after scribing, since the presence of slag may degrade the reliability of devices and inhibits wire bonding. Also, the slag can absorb some of the optical output power output of LED's.
As described in the above mentioned document, said slag is removed from said semiconductor elements by applying a protective coating, mounting the wafer on a mounting material (such as an adhesive tape), and after cutting the wafer using a laser beam, applying either a wet or a dry etch process for removing the protective coating and said slag, without affecting the mounting material.
A disadvantage of the above and other prior art methods used for separating semiconductor elements, is that it has been experienced that laser dicing of wafers results in a weaker die-strength of the single die. Especially for thin wafers, this is a critical issue. The reduced die-strength is experienced as an increased change of fracture, which can be encountered during die-handling, such as, for example, in the assembly of the die into IC-packages, e.g. die- and wire-bonding. It is noted therefore, that the above mentioned method of removing slag from a wafer during the separation process, does not effectively resolve the problems experienced with wire bonding. The reduced die-strength due to laser induced defects can be measured by a test method consisting of mechanical bending the dies in a special arrangement using four- and three-point measurements designed to focus on edge defects.
The above problem implies that handling of the product after separation is limited. It is noted for example that, in order to increase throughput, many laser dicing processes of prior art make use of cleaning methods such as high pressure cleaning. Normal cleaning methods such as high pressure cleaning cannot be applied, or are not effective in the range which can be applied, leaving debris behind on the singulated die surface. It is in particular noted that high pressure cleaning methods, where the die strength of devices is reduced as a result of the laser dicing process, may damage sensible surface structures on the device, such as vias. The debris left on the device as a result of ineffective cleaning, again causes problems such as reduced service life and degradation of reliability of the device, or decreased output power of e.g. LED's, etcetera.